Inclosed fuse



C. T. McDONALD.

INCLOSED FUSE.

APPLICATION FILED NOV-21, 1913.

Patented May 24, 1921.

(7617'6/106 TMcflana Zd UNITED STATES PATENT OFFICE.-

CIaABENCE '1. MCDONALD, OF CHICAGO ,ILLINOIS, ASSIGNOR TO CHICAGO. MFG (10., OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

INCLOSED FUSE.

Specification of Letters Patent.

Application filed November 21, 1918. Serial No. 263,472.

To all whom it may concern:

' Be it known that I, CLARENCE T. MoDoN- ALD, a citizen of the United States, residing at Chicago, in-the county of Cook and State of Illinois, have invented certain new and useful Improvements in Inclosed Fuses, of which the following is a specification.

It is well known that the operation of an inclosed fuse on heavy overload is somewhat analogous to an explosion due to the fact that the fusible element, or a portion there- 'of, melts and is converted into gas under high pressure. This gas exerts an] enormous strain upon the casing and is apt to burst the latter and injure workmen or apparatus nearby. The principal objects of this invention are to provide a novel construction by which the pressure in the fuse casing caused by the blowing of the fuse will be less than it is in ordinary refillable fuses of the air chamber type incommon use, and by which the fusible element will be caused to melt simultaneously over a relatively large area at the mid-portion of the fuse so as to effect anunusually wide break in the circuit all at once and thereby prevent arcing. I have discovered that these results may be accomplished by covering or inclosing a section or area of the fusible element having uniform cross-section with a coating or envelop of insulating material so located that the ends of the covered section will be spaced from the terminals or mounting means in the casing so as to leave exposed the intermediate portions of the fusible element which extend between the covered section and the terminals. The insulating envelop acts to retard the melting and rupture of the middle point of the section of the fusible element which it covers, and causes the whole covered section, or a relatively long section Fig. 4 is a transverse. section through the 5 8 fuse. element in the plane of line 4-4= of Fig. 3.

The casing of the fuse, and the means for securing the fuse element may be of any common or preferred construction. Inclosed or cartridge fuses now on the market are of two general types, one known aS the knife blade type (an example of which is shown in my prior Patent No. 1,311,661), the other type being known as'the ferrule type. My invention is adapted for either of said types. The exemplary embodiment shown in the drawing is a fuseof the socalled ferrule type, and the ends of the fuse element are removably mounted so that the fuse element may be replaced by the user when dlsrupted. This illustrative embodiment comprises a tubular shell 5 of insulat- 1ng materlal, two metallic heads 6 secured on opposite ends ofsuch shell, each head having therein an integral transversely dis- Patented May 24, 1921.

ate shoulder 8, two removable segmental disks 9 cooperating with such webs andshoulders to provide slots through which the ends of the fusible element 10 project. said ends being bent angularly against the outer faces of said disks, and two plugs 11 screwthreaded into the outer ends of said heads and clamping the bent-over'ends of the fuse element between the plugs and the disks. The plugs and disks are readily removable so as to permit of removal of the fuse element 10 after melting, and replacing of a new element. This construction of the casing and fuse mounting-means isv described and claimed inmy copending application Serial No. 219,597 filed February 28, 1918. Any other desired form of fuse case and mounting means may be employed.

The fuse element 10 is preferably in the form of a flat strip of fusible metal of uni form width and cross-sectional area throughout its central portion so that the currentcarrying capacity of such central portion is substantially the same at all points. A portion of the fuse element preferably located at the middle thereof is covered or inclosed by a suitable protective film, 12. A coating of paint is the form of 'inclosure or covering preferred an insulating paint of a character which will not attack or chemically react on the fusible metal being cmthe fuse element.

Without the covering material, the fuse 'ployed. The ends of the covering material are spaced a material distance from the terminals or supporting means for the ends of casing, and a coating of paint appliedto and; surrounding a section of said element and melt and rupture first on a line extending across the element at about its middle point,

and the degree of heat of the element would be gradually lower from such median line toward the ends of the element because of the median line being located farthest from the terminals which act to radiate the heat. Beginning with the melting and rupture along the said median line, the element would then melt in opposite directions away from such median line, with the result that an arc would be formed through the gap or rupture and the arc would be sustained and progressively lengthened until the gap increased to such an extent as to break the are. This arcing produces intense heat and builds up tremendous pressure of the gases within the casing tending to burst the casing.

When the mid-portion of the fuse element is covered with a non-conducting material,

inaccordance with my invention, the fuse element is not melted and ruptured first at the transverse median line", but the entire covered mid-portion, or a relatively long section of such mid-portion of the element is simultaneously melted' or consumed in the process of blowing.

A fuse constructed in accordance with my invention is particularly valuable under heavy overloads and short circuit conditions, since arcing within the casing, as above described, is most vicious under such conditions, resulting in the generation of excessive pressure within the casing and danger of bursting of the casing. My invention provides a fuse wherein the fusible element is melted and ruptured over a wide area at the same instant thereby creating a wide gap in the circuit and. efi'ectively preventing serious arcing.

l have found by actual tests that the bursting strain in the casing caused by the blowing of this fuse is' less than it is when an ordinary fuse strip is used, under conditions otherwise identical, and that casings which would be bursted by using an ordinary fuse strip will not be injured when employed with my fuse element.

I claim as my invention:

1. An inclosed fuse comprising a casing, a fusible element in the form of a fiat strip of fusible metal of uniform width and crosssection throughout its middle portion, so that its current carrying capacity is substantially the same at all points throughout such middle portion, means for mounting the ends of sa d element in the ends of said spaced inwardly from the ends of said element and from the means for mounting said element to leave exposed; the intermediate portions of the element between said coating and said mounting means.

2, An inclosed fuse comprising a casing, a fuslble element therein, means for mountlng the ends of the said element, and a coating a protective film applied to and surrounding an intermediate portion of said element spaced from said terminals and leaving exposed the end portions of said element adjacent to said terminals.

4:. A fusible element for inclosedfuses having a section thereof provided with a thin protective coating or film with exposed sections of substantial length on opposite sides of the coated section whereby said coated and uncoated sections coact upon the passage of an excessive current through the element to produce a wide break.

5. A fusible element for inclosed fuses having a section thereof provided with a thin protective coating or film with exposed sections of substantial len th on opposite sides of the coated section, t e distance between the remote ends of the coated section being less than the distance between the points of attachment of the element to the terminals of the inclosed fuse casing in which the element is designed to be. used whereby said coated and uncoated sections coact, upon the passage of an excessive current through the element, to produce a wide break.

6. An inclosed fuse comprising a casing having terminal means at its ends to secure a fusible element, a fusible element extending through said casing and attached to said terminal means, and a covering material applied to and surrounding an intermediate portion of said element spaced from said ter- I minal means and leaving exposed the end portions of said element adjacent to said terminals, said covering material acting to cause simultaneous fusion of the section of the element covered by said material and said material being relatively thin so that it portions of said elements ad acent to said terminals, said covering material afiecting chsing the radiation of heat from the mid-point of ment so as to prevent arcing, the said cover- 10 said element thereby preventing premature ing material being relatively thin so that it fusion of said mid-point and causing the enwill itself be disintegrated and broken up tire portion of said element covered by said into fine bits when the covered portion of material to come to a state of fusion at practhe element is destroyed by fusion and vatically the same time, thereby eflecting a porization. 15 disintegration or vaporization of the entire In testimony whereof I have hereunto set covered portion of the element simultanemy hand.

ously and causing a' wide break in the ele- CLARENCE T. MoDONALD. 

